Exchange 2000 why always spam attack!

Help! I always noticed that every morning we can’t send email, because our exchange mail have lot of spam, (we have sonic wall firewall) in exchange can u help me how to prevent clogging in outgoing mail, in 5.5 i never experience this only when we upgrade exchange 2000, please help. we can’t send mail, it queque only.. it clogged.. what this exchange 2000? Help please…
Ricky